The present invention is directed to a closed head drum made of thermoplastic material and blown into shape within an openable mold. The drum has roller chimes of L-shaped cross section which extend around the outer surface of the drum body adjacent the head end and the bottom end. The roller chimes are formed integrally in the drum body. The roller chimes in combination with the outer surface of the drum body form a recess or groove with the opening of the groove directed toward the adjacent end of the drum. The grooves provide engagement surfaces for a gripping and transporting tool.
As compared to drums in which prefabricated roller hoops are inserted into the blowing mold so that the hoops are welded to the drum when the extruded parison is inflated, drums incorporating roller chimes as described above have the advantage that production is much simpler. Since the roller chimes formed integrally with the drum body are component parts of the drum, they cannot be displaced during rough handling.
The blowing mold used for producing such closed head drums consists of two mold halves which are separable along a vertical plane, that is, the plane extending in the axial direction of the drum. The upper and lower region of each mold half is horizontally divided to provide mold parts which slide one into the other.
When the parison is lowered out of the extrusion head of the blowing machine, the mold halves are in the separated position so that the parison can enter into the opened blowing mold. At this time, the mold parts in each mold half which slide relative to one another are opened. After the parison is lowered in the axial direction of the drum into the mold, the two mold halves are closed. In the closed position, the mold halves clamp the previously extruded parison at what will be the head and bottom ends of the drum creating a seam across both clamped portions of the parison. The blowing process is then commenced. Molding apparatus of this type is conventional. See, for example, U.S. Pat. No. 3,985,257 for "Blow Molded Industrial Drum" and U.S Pat. No. 3,050,773 for "Process and Apparatus for Manufacturing Blown Articles". Air flowing in through a mandrel expands the parison so that it is pressed outwardly against the inner wall of the closed mold and, as a result, assumes the predetermined shape of the drum. With the upper and lower mold parts of each mold half disposed in an open position, the material of the parison enters into the recesses formed by the open mold parts. With such a mold construction, radially outwardly extending channels are formed on the container during the blow molding operation. These channels open toward the inside of the container.
Subsequently, the mold parts are moved relative to one another into a closed position. The mold parts which can be moved relative to one another are shaped to provide the roller chime configuration and the material of the channels pressed into the recesses provided by the mold parts forms the roller chimes when the mold parts are moved relative to one another. The roller chimes have an L-shaped cross section each with an outwardly extending horizontal web or leg and with a vertical leg extending from the outer end of the horizontal leg in either the upward or downward direction depending upon the location of the chimes.
The shape of the roller chime is of special significance. The gripping device for lifting and carrying the drum grasps with its tong arms under the horizontally outwardly projecting roller chime leg and behind the vertically extending leg. Accordingly, the vertical leg of the upper roller chime, that is, the chime adjacent the drum head, extends upwardly from the horizontal leg while the vertical leg of the lower roller chime, that is, the chime adjacent the bottom end of the drum, is directed downwardly from the horizontal leg. Due to the varying material distribution in the drum body, difficulties occur in the formation of the roller chimes. In the region of the dividing seams in the mold, the material of the extruded parison is doubled when the mold halves are moved to the closed position and the material has been squeezed into a clamped seam extending diametrically across the closed mold at both the top and bottom of the mold. During the blowing process, the parison is stretched and those regions which in a direction perpendicularly away from the squeezed seam become significantly thinner. In the formation of the roller chimes in the upper and lower displaceable parts of each mold half, different volumes of material are available. As a result, due to the larger amount of the material in the region of the mold dividing seams, the displaceable mold parts cannot close completely and, thus, a satisfactory formation of the roller chimes in the region of the thinner areas becomes impossible. Because of the gripping devices used in lifting and transporting the drums, a satisfactory formation of the roller chimes is required.